@windg
I think that should be fine, it was much older ones that had an issue:
https://www.reddit.com/r/MAME/comments/fws0is/where_can_i_get_chdmanexe/

The docs have info on how to use it and plenty of Youtube vids if you need them:
https://retropie.org.uk/docs/CHD-files/

@mitu Sorry about that. All of the urls where he talks about lossy chd he also use it to upload roms, so I didn't know how to refer to that person and the method he uses.

Anyway, I have edited the first post. Sorry again

I solved this in the end by downloading the neokobe collection (all 90gb for the SECOND TIME) and making CHD's with an old version of Chdman.

Nostre, how are you launching thegames? I have a 'proper' chd with the disk name 'Galaxy Force II" and then one dummy chd with the name of the entry in fmtowns_cd.xml - something like gforce2. All games will launch from the dummy chd. Now i've successfully rebuilt mess i'm not sure the check sums need to match.

So far i've found:

Galaxy force and Genocide, pu-ra-li-ra panic bomber man and Afterburner 3 are both extremely playable with decent sound

4d sports, Chase HQ, Turbo Outrun and Flashback play but with compromised sound.

Its a shame Unz is closed source.